As an experiment, I decided to see if my theory of how one could turn a shift knob without the use of an adapter would actually work in practice. I dug a chunk of curly maple out of the scrap wood box, trimmed it to a correctly sized blank, then set about turning the blank into a shift knob.
More photos of this project here:
https://rx19jones.wixsite.com/projectboxster/shift-knob
The results of my experiment;
1) This is a viable way to turn a shift knob without the use of an adapter. It is a bit tricky to make the slot exactly the right size but it's a straight forward project except for that.
2) I now have an excess curly maple Boxster shift knob. If anyone would like to have it I'd be willing to entertain offers
Cheers! - dj